The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
As fuel economy and emissions requirements become stricter, new combustion technologies are being developed. For example, engines are being developed to not only run in spark ignition mode but also a homogenous charge compression ignition (HCCI) mode. The HCCI mode involves compressing a mixture of fuel and an oxidizer to a point of auto-ignition. One of the modes may be selected based on engine speed and load. Another advanced technology is the use of lean stratified operation. Both of these technologies require relatively small fuel injection quantities in the ballistic range of less than 5 milligrams of injected fuel. The injector ballistic range is defined as the range of injected quantities for which the pintal does not contact the opening stop. Conventional fuel injection systems have a large variation of injected fuel quantity when used for metering small quantities.